In the production of minerals such as oil and gas, various laboratory procedures have been developed and used to determine lithological properties of a subterranean reservoir formation. These procedures include core flooding experiments wherein various fluids are caused to flow through a reservoir rock core sample.
Recently, computed tomography (CT) has been used to monitor core flooding experiments to aid in enhanced oil recovery and fluid mobility control. Such experiments may involve flushing a fluid through a core sample and monitoring the shape of the fluid fronts. By subtracting the images of the core samples before and after flooding, the shapes of the fluid front may be determined. The use of CT allows the interior of the core sample to be observed without disturbing the sample.
Core samples obtained by conventional coring techniques typically are three or four inches in diameter. Usually the axis of the core sample is aligned with the axis of the CT scanner and cross-sectional image slices perpendicular to the core axis are taken as the sample moves axially through the scanner.
Apparatus for positioning and moving a core sample through a CT scanner is shown and described by Vinegar et al in U.S. Pat. No. 4,583,242. The apparatus comprises a holding tube which is mounted on trolleys for axial movement through the CT scanner or, more particularly, computerized axial tomographic (CAT) scanner. The core sample is held by a sample holder concentrically within the holding tube and fluids can be injected at one end of the core sample and displaced fluids discharged from the opposite end for conducting core flooding experiments.
The above and similar apparatus set-ups are well suited to the performance of horizontal core flow tests since the axis of the CT scanner is oriented horizontally. However, some laboratory flow tests may require the fluids to flow vertically through the core sample (top to bottom or bottom to top) to more closely simulate processes occurring in petroleum reservoirs. This presents a problem when it is desired to carry out these tests on-line in a CT scanner so that the fluids can be imaged as they flow vertically through the core. Turning conventional horizontal core flow set-ups on end is undesirable for several reasons. The imaged cross-section of the core sample will be rectangular and this can cause false artifacts in the image. For best results the object being scanned should be circular or round. In addition, the cross-sectional area of the core sample will vary from slice-to-slice because the image will be taken along different chordal planes as the core sample is indexed through scanner in a direction perpendicular to its axis. Consequently, a need exists for an apparatus and method for conducting and imaging vertical core flow tests on-line in a horizontal axis CT scanner.